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    Re: Using star-star distances
    From: Ken Gebhart
    Date: 2008 Sep 23, 22:26 -0500

    George,
    
    As an aside to this discussion, I am wondering what the status of
    EBBCO now is.  In about 1972, I set out to find the East Berks Boat
    Co. (EBBCO).  After asking several shopkeepers in town, I was
    directed to John Weatherlake's home as the most probable location.
    There, he showed me how he assembled the sextants in his garage.  My
    understanding as of 2 years ago is that they are still in production,
    but on a larger scale than his garage could afford, and under
    different names than EBBCO.  The name Antares comes to mind, possibly
    as Plastimo in France names it.  Anyway, I , and I think some list
    members, might be interested to know more about this sextant today.
    Any information you may have, as a countryman of Mr. Weatherlake,
    will be appreciated.
    Ken
    On Sep 23, 2008, at 2:36 PM, George Huxtable wrote:
    
    >
    > Frank wrote-
    >  In some of my recent sextant calibration tests, I've had the
    > | pleasure of watching, in real time, the calibration of a plastic
    > sextant
    > | glide up two minutes of arc postive for a couple of minutes (of
    > time) then
    > | drift in the opposite direction until it was zero and then
    > negative by a
    > | couple of minutes of arc. Something like that simply cannot be
    > corrected
    > in
    > | live navigation.
    >
    > ==========================
    >
    > That's interesting, and rather a surprise to find such extreme
    > bad-behaviour. Was the index error similarly unstable, or did the
    > index
    > error stay put while the calibration changed? What were the
    > conditions of
    > the test? Had the instrument been given any time to stabilise, in
    > temperature? Presumably, the instrument had been checked-over to
    > ensure that
    > no mirrors or brackets were at all wobbly
    >
    > My own experience of plastic sextants has been confined to just one
    > make;
    > various models of the Ebbco design. And I must say that I've never
    > been
    > aware of such wild short-term changes in calibration as Frank
    > describes.
    > Such changes would have been quite apparent, in distorting a
    > sequence of
    > altitude observations. Nor have I ever been aware of measurable
    > drifts in
    > index-error, which I have always checked before and after such a
    > sequence. I
    > would never expect to measure angles to better than an arc-minute
    > or so with
    > an Ebbco, however.
    >
    > Frank's comments, applying to an unspecified "plastic sextant", tar
    > all such
    > sextants with the same brush. It would be fairer, and more useful
    > to others,
    > for him to actually "name names", and specify the type of plastic
    > sextant
    > which he found to be so faulty.
    >
    > George.
    >
    > contact George Huxtable, now at george@hux.me.uk
    > (switched from george@huxtable.u-net.com)
    > or at +44 1865 820222 (from UK, 01865 820222)
    > or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    >
    >
    >
    
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